Re: [PATCH v3] VT-d: add iommu=igfx option to workaround graphics issues

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/08/15 10:11, Ting-Wei Lan wrote:
> When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake
> devices, It is possible to encounter graphics issues that make screen
> unreadable or crash the system. It was reported in freedesktop bugzilla:
>
> https://bugs.freedesktop.org/show_bug.cgi?id=90037
>
> As we still cannot find a proper fix for this problem, this patch adds
> iommu=igfx option to control whether Intel graphics IOMMU is enabled.
> Running Xen with iommu=no-igfx is similar to running Linux with
> intel_iommu=igfx_off, which disables IOMMU for Intel GPU. This can be
> used by users to manually workaround the problem before a fix is
> available for i915 driver.
>
> Signed-off-by: Ting-Wei Lan <lantw44@gmail.com>
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Wei: I think this is a candidate for inclusion into 4.6

~Andrew

> ---
> Changed since v2:
>   * Make no-igfx available for all Intel devices, not just Calpella/Ironlake
> Changed since v1:
>   * Replace igfx_off with igfx
>
>  docs/misc/xen-command-line.markdown  | 11 ++++++++++-
>  xen/drivers/passthrough/iommu.c      |  3 +++
>  xen/drivers/passthrough/vtd/quirks.c |  3 +++
>  xen/include/xen/iommu.h              |  2 +-
>  4 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
> index 13f03ad..486e53b 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -793,7 +793,7 @@ debug hypervisor only).
>  > Default: `new` unless directed-EOI is supported
>  
>  ### iommu
> -> `= List of [ <boolean> | force | required | intremap | qinval | snoop | sharept | dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug | verbose | debug ]`
> +> `= List of [ <boolean> | force | required | intremap | qinval | snoop | sharept | dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug | igfx | verbose | debug ]`
>  
>  > Sub-options:
>  
> @@ -867,6 +867,15 @@ debug hypervisor only).
>  >> ignored (normally IOMMU setup fails if any of the devices listed by a DRHD
>  >> entry aren't PCI discoverable).
>  
> +> `igfx` (VT-d)
> +
> +> Default: `true`
> +
> +>> Enable IOMMU for Intel graphics devices. The intended usage of this option
> +>> is `no-igfx`, which is silimar to Linux `intel_iommu=igfx_off` option used
> +>> to workaround graphics issues. If adding `no-igfx` fixes anything, you
> +>> should file a bug reporting the problem.
> +
>  > `verbose`
>  
>  > Default: `false`
> diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
> index cc12735..966cc66 100644
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -47,6 +47,7 @@ bool_t __read_mostly force_iommu;
>  bool_t __hwdom_initdata iommu_dom0_strict;
>  bool_t __read_mostly iommu_verbose;
>  bool_t __read_mostly iommu_workaround_bios_bug;
> +bool_t __read_mostly iommu_igfx = 1;
>  bool_t __read_mostly iommu_passthrough;
>  bool_t __read_mostly iommu_snoop = 1;
>  bool_t __read_mostly iommu_qinval = 1;
> @@ -87,6 +88,8 @@ static void __init parse_iommu_param(char *s)
>              force_iommu = val;
>          else if ( !strcmp(s, "workaround_bios_bug") )
>              iommu_workaround_bios_bug = val;
> +        else if ( !strcmp(s, "igfx") )
> +            iommu_igfx = val;
>          else if ( !strcmp(s, "verbose") )
>              iommu_verbose = val;
>          else if ( !strcmp(s, "snoop") )
> diff --git a/xen/drivers/passthrough/vtd/quirks.c b/xen/drivers/passthrough/vtd/quirks.c
> index 69d29ab..92cff1d 100644
> --- a/xen/drivers/passthrough/vtd/quirks.c
> +++ b/xen/drivers/passthrough/vtd/quirks.c
> @@ -72,6 +72,9 @@ int is_igd_vt_enabled_quirk(void)
>  {
>      u16 ggc;
>  
> +    if ( !iommu_igfx )
> +        return 0;
> +
>      if ( !IS_ILK(ioh_id) )
>          return 1;
>  
> diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
> index 8eb764a..29eed51 100644
> --- a/xen/include/xen/iommu.h
> +++ b/xen/include/xen/iommu.h
> @@ -29,7 +29,7 @@
>  
>  extern bool_t iommu_enable, iommu_enabled;
>  extern bool_t force_iommu, iommu_verbose;
> -extern bool_t iommu_workaround_bios_bug, iommu_passthrough;
> +extern bool_t iommu_workaround_bios_bug, iommu_igfx, iommu_passthrough;
>  extern bool_t iommu_snoop, iommu_qinval, iommu_intremap;
>  extern bool_t iommu_hap_pt_share;
>  extern bool_t iommu_debug;